|Summary=Funtoo Linux prefers FFmpeg. Some enlightenment about our choice and why we prefer this or could switch to alternative in future.

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|Author=Oleg, Mgorny

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|Maintainer=Oleg

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|Reference Bug=FL-844

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}}

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== Introduction ==

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FFmpeg and Libav are library sets for multimedia decoding (and more). Both libraries expose similar API and features.

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Both project have common origins and diverged only recently. The developers share the same bad coding practices causing permanent lack of API and ABI stability, therefore requiring frequent rebuilds of reverse dependencies.

Worse than that, after the split projects use colliding SONAMEs for libraries with potentially different ABI. This means that after switching from one implementation to another, the reverse dependencies may become broken instantly (preserved-libs doesn't help) and need to be rebuilt ASAP.

Many packages for video decoding, are done via FFmpeg or Libav. Differences between FFmpeg and Libav can have a major impact on its behavior: the number of files it can decode, whether it decodes correctly, what video and audio filters are provided, network behavior, and more.

Gentoo supports both ffmpeg and libav, with a preference towards libav. The preference is caused by package order in virtual/ffmpeg — when no other circumstance affects the package choice, Portage will prefer libav. However, if ffmpeg is already installed or a package incompatible with libav is requested, Portage will use ffmpeg instead.

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There are two major technical issues with this design:

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==== Configuração de Pacote do Kernel ====

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# there is no technically correct way of forcing rebuilds on ABI changes — subslot dependencies do not work with virtuals or || () deps,

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# there is no way of forcing rebuilds when switching from libav to ffmpeg, and the other way around.

Funtoo has no plan to change default FFmpeg, it only needs to mask libav in the profiles. Then dependencies on updated packages will unconditionally use FFmpeg. Eventually Funtoo will want to remove virtual/ffmpeg and depend on media-video/ffmpeg:0= directly in forked packages.

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=== Gentoo ===

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<console>

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There is a planned Gentoo change which will eventually replace virtual/ffmpeg and explicit || () deps with 'libav' USE flag. The flag will be added to all packages that support both FFmpeg and libav. When the flag is enabled, the package will use libav; otherwise it will use FFmpeg. The choice of flag name is forced by the fact that USE=ffmpeg is already used as generic ffmpeg-or-libav flag.

The change may also eventually make it possible to install FFmpeg and libav side-by-side. Until then, the flag state would involve 'strong' preference of one implementation over the other, and user will have to change USE=libav as a global flag. '''Installing a package that supports only one of the two implementations will result in blocker that needs to be handled manually'''.

In 2011, parts of the FFmpeg developers were unhappy about the FFmpeg leadership, and decided to take over. This didn't quite work out. Apparently Fabrice Bellard, original FFmpeg developer and owner of the ffmpeg.org domain name, decided not to hand over the domain name to the new maintainers. So they followed Plan B, and forked FFmpeg, resulting in Libav. Since then, Libav did its own development, and completely ignored whatever FFmpeg did. FFmpeg, on the other hand, started to merge literally everything Libav did.

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The reason for the fork is most likely that the developers hate each other. While this formulation seems somewhat sloppy, it is most likely the truth. To this date, the #libav-devel IRC channel still has Michael Niedermayer (the FFmpeg maintainer since 2004 according to Wikipedia) on their ban list (similar misbehavior is exhibited by some FFmpeg developers). There is little to no cooperation between the two projects.

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==== Building the Kernel ====

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More about FFmpeg's history and the fork incident can be found on Wikipedia

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{{Fancynote|1=

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See [[Funtoo Linux Kernels]] for a full list of kernels supported in Funtoo Linux. We recommend <code>debian-sources</code> for new users.}}

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=== Situation today ===

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{{fancyimportant|1=

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FFmpeg has more features and slightly more active development than Libav, going by mailing list and commit volume. In particular, FFmpeg's features are a superset of Libav's features. This is because FFmpeg merges Libav's git master on a daily basis. Libav on the other hand seems to prefer to ignore FFmpeg development (with occasional cherry-picking of bug fixes and features).

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<code>debian-sources</code> with <code>binary</code> USE flag requires at least 14GB free in <code>/var/tmp</code> and takes around 1 hour to build on a Intel Core i7 Processor.}}

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Some Linux distributions, especially those that had Libav developers as FFmpeg package maintainers, replaced FFmpeg with Libav, while other distributions stick with FFmpeg. Application developers typically have to make sure their code works with both libraries. This can be trivial to hard, depending on the details. One larger problem is that the difference between the libraries makes it hard to keep up a consistent level of the user experience, since either library might silently or blatantly be not up to the task. It also encourages library users to implement some features themselves, rather than dealing with the library differences, or the question to which project to contribute.

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Let's emerge our kernel:

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FFmpeg and Libav developers also seem to have the tendency to ignore the damage their rivalry is causing. Apparently fighting out these issues on the users' backs is better than reconciling. This means everyone using these libraries either has to suffer from the differences, or reimplement functionality that is not the same between FFmpeg and Libav.

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<console>

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{{FLOPFooter}}

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(chroot) # ##i##emerge -1 @kernel

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</console>

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{{Important|Right now, the <code>-1</code> option is required to not add our <code>@kernel</code> set to <code>world-sets</code>. This allows you to emerge it independently from @world. If you forget to use this option, edit <code>/var/lib/portage/world-sets</code> and remove the <code>@kernel</code> line. This will prevent kernel updates from being included in @world updates.}}

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Note that while use of the <code>binary</code> USE flag makes installing a working kernel extremely simple, it is one part of Funtoo Linux that takes a ''very'' long time to build from source, because it is building a kernel that supports ''all'' hardware that Linux supports! So, get the build started, and then let your machine compile. Slower machines can take up to several hours to build the kernel, and you'll want to make sure that you've set <code>MAKEOPTS</code> in <code>/etc/portage/make.conf</code> to the number of processing cores/threads (plus one) in your system before starting to build it as quickly as possible -- see the [[#/etc/portage/make.conf|/etc/portage/make.conf section]] if you forgot to do this.

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{{fancynote|NVIDIA card users: the <code>binary</code> USE flag installs the Nouveau drivers which cannot be loaded at the same time as the proprietary drivers, and cannot be unloaded at runtime because of KMS. You need to blacklist it under <code>/etc/modprobe.d/</code>.}}

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{{fancynote|For an overview of other kernel options for Funtoo Linux, see [[Funtoo Linux Kernels]]. There may be modules that the Debian kernel doesn't include, a situation where [http://www.funtoo.org/wiki/Funtoo_Linux_Kernels#Using_Debian-Sources_with_Genkernel genkernel] would be useful. Also be sure to see [[:Category:Hardware Compatibility|hardware compatibility]] information.}}

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Once <code>emerge</code> completes, you'll have a brand new kernel and initramfs installed to <code>/boot</code>, plus kernel headers installed in <code>/usr/src/linux</code>, and you'll be ready to configure the boot loader to load these to boot your Funtoo Linux system.

Building the Kernel

See Funtoo Linux Kernels for a full list of kernels supported in Funtoo Linux. We recommend debian-sources for new users.

Important

debian-sources with binary USE flag requires at least 14GB free in /var/tmp and takes around 1 hour to build on a Intel Core i7 Processor.

Let's emerge our kernel:

(chroot) # emerge -1 @kernel

Important

Right now, the -1 option is required to not add our @kernel set to world-sets. This allows you to emerge it independently from @world. If you forget to use this option, edit /var/lib/portage/world-sets and remove the @kernel line. This will prevent kernel updates from being included in @world updates.

Note that while use of the binary USE flag makes installing a working kernel extremely simple, it is one part of Funtoo Linux that takes a very long time to build from source, because it is building a kernel that supports all hardware that Linux supports! So, get the build started, and then let your machine compile. Slower machines can take up to several hours to build the kernel, and you'll want to make sure that you've set MAKEOPTS in /etc/portage/make.conf to the number of processing cores/threads (plus one) in your system before starting to build it as quickly as possible -- see the /etc/portage/make.conf section if you forgot to do this.

Note

NVIDIA card users: the binary USE flag installs the Nouveau drivers which cannot be loaded at the same time as the proprietary drivers, and cannot be unloaded at runtime because of KMS. You need to blacklist it under /etc/modprobe.d/.

Once emerge completes, you'll have a brand new kernel and initramfs installed to /boot, plus kernel headers installed in /usr/src/linux, and you'll be ready to configure the boot loader to load these to boot your Funtoo Linux system.